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You are watching: Will a 5000 watt generator run a welder


What size generator do I need to run a welder?

I get asked that a lot.

There are good reasons why it makes sense.

You need to repair a gate that’s not close enough to household powerA friend’s truck is broken down out on the trailYou want to build a greenhouse in your garden

But if it’s too small, you could damage or kill your expensive welder.

Too big, and it may cost too much to run, be hard to move, and take up too much room.

How to Figure Out What Size Generator For Your Welder

This question usually takes one of these forms, for example:

What size ggenerator do I need for a 180 amp welder?Will a 7,000-watt generator run a welder?How big of a welder can you run with a generator of X size?

These are actually all the same questions. You’re just asking it from different viewpoints.

This Is How You Do It

Generators, like welders, come in lots of different sizes. There are a lot of features and options available. And you’ll need to decide if you want 120-volt output, 240 volts, or both.

The trickiest thing to watch out for is that generators are rated in total WATTS of power output, but welders are rated for output AMPERAGE.

That means you need to figure out how many watts a welder needs to produce its rated amps.

How Many Watts Does Your Welder Use?

There’s a very basic math equation to move back and forth between volts, amps, and watts:

Volts x Amps = Watts

Volts: The technical definition is “a measurement of the difference in electrical potential between two points.”

Think of volts in the same way you think of water pressure. It’s the available “push” that gets the electricity going.

Amps: Amperes are a way to measure the flow of electrical current.

Keeping with our water supply analogy, think of amps as the rate of flow in the pipes, fast or slow.

Watts: A watt measures heat energy. As electrons flow through the circuit, friction makes heat, measured in watts.

So what you need is the voltage the welder uses, multiplied by the input amps of the welder.

Find Your Welder’s Input Power

Step 1: Find the power & current levels

First, you need to know what power and current levels your welder needs to run. A commonplace to find this info is in the manual.

Here’s an example from the manual for the PrimeWeld Stick 160.

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Checking the specifications, once again, there are numbers here for “Current Input”. This label is easier to work with than some because it gives both input voltage and the input current needed by the welder.

It’s easy to figure out how much power you need in watts from a generator for your welder. For the 140-amp version, multiply:

120 volts input x 23 amps = 2,760 watts

That’s only the BASIC number, however. It’s characteristic of power tools to use much more power to start than it takes to keep them running.

Generator makers advise adding up to 30 percent to the running watts to account for starting devices.

2,760 watts x .30 = 828 watts

Add this 30 percent safety margin to the basic running figure of 2,760 watts:

2,760 + 828 = 3,588

This amounts to 3,600 watts. This welder will need a generator rated at 2,800 operating watts, with a peak rating of 3,600 watts.

Take away notes:

DON’T FORGET to add specified tolerance, like our example was plus or minus 15 percent. ALWAYS ADD THE TOLERANCE IN.REMEMBER TO ADD 30 percent to your total wattage to cover the starting surge. The exception to this rule is if you’re using a value known as “I1max“. See the next section for more information.Input Values Can Have Other Names too

Sometimes there are several different types of electrical ratings. You may not have a rating on the label that’s specifically called “input voltage” or “input current,” but there are other names for them.

No need to be confused, however. Check for values with these names instead:

Input VoltageMax PowerMax VoltageV max or VmaxU max or UmaxU1maxInput CurrentMax AmperageMax CurrentA maxI maxI1max

Note that choice 5 in both cases has a notation of 1max. This name specifically indicates main input power.

I2 or I2max means output power.

The I1max rating is already adjusted for surge or starting watts. If you calculate with I1max, you already have your maximum starting watts rating WITHOUT a need to add 30 percent.

Another unit you sometimes see on a generator for welders is the Kilovolt Amp or KVA.

For this unit 1,000 volts x 1 Amp = 1 KVA, the same as 1 Kilowatt (Kw).

Remember: Volts x Amps = Watts

Because 1 KVA = 1 Kw, a generator that makes 6 KVA of peak power is also rated at 6 kW.

Power Supply Differences Between Inverters & Transformers

One important choice is whether your welding machine is powered by a transformer or is an inverter welder. This matters because with generators for welders, there is a quality called “dirty power.”

“Dirty Power” means small and repeated fluctuations in the power level as the engine runs.

These fluctuations in power are called “harmonic distortion” and measured in units of Total Harmonic Distortion, or THD. It’s presented as a percentage, for instance, “5 percent THD.”

Transformer-powered welders are quite forgiving of dirty power from a generator. Nearly any modern generator can run a transformer-powered welder.

The problem is with inverter-powered machines. Commonly called IGBT and MOSFET welders, they have problems with dirty power because their control circuits are easily damaged by harmonic distortions in the power supply.

Without getting too technical, these designs use capacitors to filter out distortion, smoothing the power supply. Another benefit of inverter power is the welder itself can be lighter.

A lot of modern generators are designed with inverter filters, making them safe for inverter-powered welders.

If you have a transformer-powered welder, THD isn’t a problem, but if you want to run a computer, anything digital, or an IGBT or MOSFET welder, you need to be below 6 percent THD.

Other Factors Affecting Your Choice

High Altitude Issues

At high altitudes, there’s less oxygen. Gasoline, diesel, and propane engines run less efficiently, making less power. Your welding generator will make less wattage at high altitudes than it would at sea level. Generator makers advise planning on a 3.5 percent power loss for every 1,000 feet of elevation.

Depending on the elevation, it could be barely noticeable, or it could be a lot less power. Generator makers offer high-altitude kits to help.

Extra Tools and Equipment

If you need to run extra tools like saws, grinders, drills and the like, you need to add at least another 2,000 watts to the capacity because many grinders and reciprocating saws take as much as 1,800 watts to operate.

Also, consider fans, heaters, and lighting. It may actually be cheaper to buy a smaller generator for these accessories than one large one to run both your welder and extra tools.

Here’s a partial list of common devices and their power demands:

ApplianceRunning WattsStarting Watts
Coffee Maker17500
625W Microwave625800
Single 60W equivalent CFL bulb150
Radio50-2000
Room Air Conditioner: 10,000 BTU15002200
Small Appliance2001700
8in. Bench Grinder14002500
Pressure Washer: 1 HP12003600
7-1/4in. Circular Saw14002300
Electric Chain Saw: 14in. Bar, 2 HP11000
10in. Table Saw18004500
Drill: 3/8in., 4 Amps440600
Drill: 1/2in., 5.4 Amps600900
Portable Heater (Kerosene, Diesel Fuel): 90,000 BTU500725
Battery Charger: 60 Amp with 250 Amp Boost1500/57500
Laptop650
LCD Computer Monitor250
Inkjet Printer150
Tablet120
Cell Phone Charger100

How Long Is the Run Time?

This is how long a generator can run at full demand, with a full tank of fuel. Some can run as long as 8-10 hours, while some big generators might only last a couple of hours between refills if they’re working hard.

Noise

Generators are loud, although generally not as loud as some tools and vehicles are. There are also exhaust fumes to consider, with the danger of carbon monoxide. You can’t put a generator inside safely, and they all have labels telling you not to do this.

You need to make sure it’s ventilated well, protected from collisions or dropped items, cords can reach your work area safely, and noise won’t be a problem where it’s sitting.

Check its dB rating to see how loud it is. Anything over 90 dB is damaging to hearing. 120-decibel ratings and above are equivalent to literally deafening sounds like drag racers, artillery, jet aircraft, and hunting rifles.

Placement

This chart gives some National Electrical Manufacturers (NEMA) recommendations on extension cord length. Whenever possible, plug devices directly into the generator.

Your coffee maker can brew until you take a break, then you can pour a cup once you walk over and shut off the generator.

Total Wattage10 gauge cord12 gauge cord14 gauge cord16 gauge cord
2,400250 feet150 feet100 feet75 feet
4,800125 feet75 feet50 feet25 feet
7,20060 feet35 feet25 feet10 feet
9,60030 feet15 feet10 feet0
12,00015 feet000

Generators with 4Kw or more running wattage can easily weigh over two hundred pounds. Wheel kits, wheelbarrow-style handles, and lifting bales for hooks are all items that make things a lot easier when positioning such a heavy piece of equipment.

Related: What Size Wire for Welder Extension Cords?

Generator Sizing Chart for Welders

Here’s a quick reference table I put together to give you an idea of what size generator you should be aiming for, depending on your welder’s current level.

Welder Current LevelMinimum Generator SizingRecommended Generator Size
Up to 160A7kva 0r 7000 watts8000+ watts
180–200A8kva or 8000 watts10,000+ watts
210-250A13kva or 13,000 watts15,000+ wats

Best Generators for Welders

I’m going with substantial portable generators here.

You don’t want your generator working too hard, running flat out. It’s easier on your new power plant if it’s not breathing hard to get the job done.

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Cleaner and more consistent power, less wear, and longer life are the rewards of a small extra investment.